1. Field of the Invention
The present invention relates to a wire bonding apparatus and more particularly to a wire pay-out control mechanism.
2. Prior Art
Conventional wire pay-out control mechanisms for wire bonding apparatuses are described in, for example, Japanese Patent Application Laid-Open (Kokai) No. H7-283264 and Japanese Utility Model Registration No. 2513442. In these structures, a tension-applying means that applies tension to the wire supplied to the capillary is provided at a point beneath the spool on which the wire is wound. Tension is applied to the wire by a gas that jets out from the tension-applying means, thus forming a bowed portion in the wire between the spool and the capillary.
In the above structures, a wire pay-out sensor is installed above the tension-applying means so as to be positionally apart from gas-jet-out side of the tension-applying means. When this wire pay-out sensor ceases to sense the wire, the spool is caused to rotate so as to pay-out the wire; and when the wire pay-out sensor senses the wire, the rotation of the spool is stopped. Furthermore, a wire-end detection sensor is disposed on the gas-jet-out side of the tension-applying means. When this wire-end detection sensor senses the wire, it is determined that the wire on the spool has been all consumed.
As seen from the above, in the above prior art, wire pay-out is initiated when the wire is moved away from the wire pay-out sensor. Accordingly, wire pay-out is frequently performed, resulting in that the pay-out of the wire becomes unstable. Furthermore, as a result of this and as a result of the fact that the spool is rotated and the wire is paid out until the wire pay-out sensor senses the wire, the wire tends to vibrate by the gas jetting out of the tension-applying means. Thus, there is a chance that erroneous sensing occurs. If such erroneous sensing occurs, the wire would be paid out more than it is actually necessary.
Accordingly, the object of the present invention is to provide a wire bonding apparatus that can constantly pay out a fixed amount of the wire and prevent the wire from being paid out more than it is necessary. In the present invention, this is done not as a result of detection of the stopping of the pay-out of the wire from the spool but as a result of a constant wire-pay out whenever the amount of bowing of the wire in the area of the tension-applying means becomes insufficient.
The above object is accomplished by a unique structure of the present invention for a bonding apparatus, which comprises:
a spool motor that causes the rotation of a spool around which a wire is wound,
a tension-applying means disposed beneath the spool,
a wire pay-out sensor that is disposed at a position away from the gas-jet-out side of the tension-applying means and senses that the wire supply is insufficient,
a wire-end detection sensor disposed on the gas-jet-out side of the tension-applying means and senses that the supply of the wire from the spool has stopped, and
a control device that performs a control action so that the spool motor is rotated by a predetermined fixed amount when the wire is sensed by the wire pay-out sensor.
In the above-described structure, the control device includes a quantum limit circuit into which a predetermined number of pulses are inputted; and when the start signal from the wire payout sensor is inputted into the quantum limit circuit, the quantum limit circuit outputs pulses that cause the spool motor to rotate, with these pulses being equal to the predetermined number of pulses.